Sparking plug



Feb. 22, 1944. c. M. CARINGTON ETAL 2,342,350

SPARKING PLUG Filed Nov; 20, 1942 /-:ZZ CHARLES M. CARRINQTON Patented Feb. 22, 1944 SPABKIN G PLUG Charles Molyneux Carington and George William Shoobert, London, England Application November 20, 1942, Serial No. 466,264 In Great Britain February 9, 1942 3 Claims.

Owing to the high duty required of many modern internal-combustion engines, difliculties are encountered from the overheating of the sparking-plugs, leading to pre-ignition and short working life of the plugs, and it is the object of this invention to provide a construction of plug whereby the working temperature of the firingpoints andthe adjacent end of the insulator is reduced.

Modern high-duty plugs usually have a ceramic insulator, and the present practice is to keep the earth-points as short as possible in order to reduce their temperature; in order to keep them short the hole through the inner end of the body to the edge of which the wires are attached has been made to the smallest possible diameter and in some cases has been provided with an inwardly directed flange to carry the earth-points, but we consider that this is not the governing factor and have devised a novel construction of plug in which the parts affected by heat are exposed as fully as possible to the gases in the combustion chamber of the engine, so that cool gases entering the combustion chamber may have free access to the end of the insulator and the firing-points, and also that radiation of heat from these parts shall not be restricted by their enclosure within heated parts of the plug body.

This invention accordingly comprises a sparking-plug having a ceramic insulator, wherein the body of the plug is so shaped as to provide an open space around the end of the insulator and the firing-point for the purpose of reducing the temperature of these parts.

Preferably the invention is applied to sparking-plugs in which the insulator material is sintered aluminium oxide, or a material containing not less than 80% of alumina, with a core of metal of high heat-conductivity and firing-points made of platinum or an alloy of platinum in the form of wire of small cross-sectional area.

According to another feature of this invention, the end of the sparking-plug body which is in communication with the combustion chamber is formed with a tapered countersink, or bellmouth, with the end of the insulator projecting beyond the minimum diameter of the opening so that it is freely exposed to the cool gases'entering the combustion chamber and also can radiate heat freely.

In the accompanying drawing, which illustrates one construction of plug according to this invention:

Figure 1 is an elevation of part of a plugbody, shown partly in section on the line l-l of Figure 2,

Figure 2 is an end view of a complete plug, and Figure 3 is an elevation, partly in section on the line 3-3 of Figure 2, of one end of a sparking-plug.

Referring to the drawing, the plug-body N is generally of the normal construction, with a screw-threaded portion I I engaging the cylinder wall with the end I2 of the interior of the plug open to the combustion chamber.

The central insulator I2 is a ceramic material containing not less than of alumina, with a central electrode forming a core which is of high conductivity metal in intimate contact with the material of the insulator. The firing-point 13 on the end of the electrode is a wire of small cross-sectional area made of platinum or an alloy thereof which is capable of withstanding the temperatures to which the plug is subjected in use. The open end l2 of the plug-body is formed internally as a tapered counter-sink or bellmouth M as shown most clearly in Figure l, and the end of the insulator I2 projects beyond the minimum diameter of the openin so that it is freely exposed to the cool gases entering the combustion chamber and also can radiate heat freely.

The earth-points [5 which are also in the form of wires of small cross-sectional area, may be one or more in number and extend to near the firing-point I3 from the body of the plug. In order that their length shall not be excessive, small projections I6 are left on the inner surface of the bell-mouth whereon these earth-points are secured in any convenient manner. These projections 16 are of small circumferential extent and do not materially interfere with the access of the cool gases to the end of the insulator l2, firing-point l3 and earth-points 15.

In the case of the bell-mouth the form of the internal cavity may be that of a part of a sphere, so that it can be produced by means of two milling cutters shaped as parts of a sphere and separated by the distance required to leave the two projections to which the earth wires may be attached.

The free exposure of the end of the insulator, as compared with the construction now in use for high-duty plugs, has ben found, by a long series of experiments and tests, to achieve a satisfactory lowering of the temperature of the insulator and firing-points, thereby rendering it possible to increase the duty of the engine or,

ins-plug or to combine these two benefits.

We claim: 1. In a sparking-plug the combination of a central electrode, a ceramic insulator surroundin: it, a firing-point on said electrode extending from said insulator, a plug-body containing said insulator and formed with a hell-mouth surrounding the firing-point and adjacent part of the electrode, internal projections of small circumferential extent in said bell-mouth and earth'- polnts carried on said projections.

2. In a sparking-plug the combination of a central electrode, a ceramic insulator surrounding it, a firing-point on said electrode extending from said insulator, a plug-body containing said insulator and having the open end of the plugbody formed to a substantially hemispherical shape by a milling operation, internal projections of small circumferential extent in said hemispherical opening and earth-points carried on said projections.

3. In a sparking-plug the combination of a central electrode of highly heat conductive metal, a ceramic insulator containing not less than alumina surrounding said electrode and in intimate contact therewith, a firing-point of platinum or an alloy thereof in the form of wire of small cross-sectional area secured on said electrode and extending from said insulator, a plugbody containing said insulator and formed with i a substantially hemispherical bell-mouth to provide an open space around the firing-point and adjacent part of the insulator, internal projections on said bell-mouth of small circumferential extent and earth-points carried on the said projections.

CHARLES MOLYNEUX CARINGTON. GEORGE WILLIAM SHOOBERT. 

